Quartz crystal clocks are based on-

CONCEPT:

• Quartz crystal clocks:​ They are used to measure time.
  • Quartz crystal clocks have an accuracy of 1 second every 109 seconds.
• It works on the principle that an oscillating emf develops in one pair of faces of the crystal when a variable pressure is applied on another pair of faces of the crystal perpendicular to the first one.

EXPLANATION:

Quartz crystal clock based on Piezoelectric effect.

• Piezoelectric effect: An oscillating emf develops in one pair of faces of the crystal when a variable pressure is applied on another pair of faces of the crystal perpendicular to the first one.
• Compton effect: Scattering of a photon by an electron, that results in a decrease in energy (or increase in wavelength) of the photon.
• Photoelectric effect: If electromagnetic radiation strikes a material and electron emission takes place, then this phenomenon is called the photoelectric effect

Hence option 1) is correct.